Global Warming: Greenland When It's HotThe Arctic frontier is changing faster than anywhere else on Earth—in ways both spectacular and terrifying. The sea ice is melting, the glaciers are crumbling, and scientists and adventurers are scrambling like mad just to keep up. Text by Paul Bennett

An ablation zone such as JAR is a liminal place where the imperceptible movement of the ice cap becomes freakishly perceptible. In a few short yards the ice goes from rink smooth to a tangle of hummocks, ice cliffs, meltwater lakes, and all forms of deadly holes opening and closing as the ice cap moves toward the sea. In the past few years the weather station has migrated half a mile and now sits in the middle of a crevasse field.

As I followed Steffen's established route through this invisible minefield with the rest of the research team, I remembered the professor's warning that rising temperatures have made the ice unstable. "If you feel your Ski-Doo fall out from beneath you, put your arms out like this," he said, shoving his arms straight to each side like a scarecrow. "It saved me once."

The work at JAR2 goes slower than expected, which is worrisome. The longer we stay out here, the more the ice melts and the greater the chance that one of these holes will open up near us. Steffen had hoped to be done early and to head back to Swiss Camp before the heat of the day. But by noon he has drilled ten holes to no avail.

The air is warmer at JAR2's lower elevation, and the winds nonexistent. Everyone pulls off their ski masks and hats. Restless, NASA scientist Zwally decides to take a little stroll out to the hummocks that surround JAR2. I tag along. "Be careful," Steffen intones as we pad softly away. He sticks his arms out to remind me about crevasses.

Zwally has been coming to Greenland for 13 years, nearly as long as Steffen. His role is to monitor the movement of the ice cap by maintaining eight GPS stations at various elevations and distances from Swiss Camp. His data on rising ice velocities are as disturbing as Steffen's on rising temperatures. In 2002 the pair wrote a paper that shocked the scientific community and found its way into the New York Times. In it they theorized that meltwater on the surface of the ice cap was draining through enormous moulins down to the rock 3,937 feet (1,200 meters) below. There the water acted as a lubricant, causing the ice cap to slide more quickly into the sea. Zwally's GPS measurements show that the moulins' effect is more than just a theory: The Jakobshavn Glacier is moving into the sea twice as fast today as it was ten years ago.

Zwally grumbles something over his shoulder about following in his footsteps. I can see indentations in the light snow, evidence of cracks and mini-crevasses. Zwally reads the terrain and putters a path around them. I dutifully follow. After a quarter mile of padding along carefully like old men in a convalescent home, Zwally stops on a mound of glistening ice that slopes downward. In the distance lies a brilliant blue meltwater lake sitting in a bowl of white ice towers. It's stunning, and I make a joke about developing condos along its edge. But Zwally's mind is elsewhere. He's thinking about moulins, which some scientists believe form under these lakes. No one is exactly sure because moulins are, hands down, the most dangerous phenomenon on the ice, and few people have ever gotten near enough to study them. If Zwally's theory is correct, some may be a mile (2 kilometers) deep, filled with mad-rushing water. One misstep and you might be on your way to the bottom of the ice cap. Zwally relates a story about David Drewry, a British glaciologist who fell into a meltwater stream and was whisked along for several hundred yards, stopping short of a moulin by a mere hundred yards. A colleague of Steffen's wasn't so lucky and disappeared for good into one of these holes.

Zwally is fascinated by moulins because they may be a localized mechanism for accelerating the effects of global climate change. With temperatures slightly warmer than freezing, meltwater is an important tool for transmitting heat around the ice sheet. When it sits in a lake, its effect is limited to the ice directly proximate to it. But when it moves, it spreads heat across a large area. Moulins may move meltwater—and the heat it carries—across great distances, with profound effects on the health of the glaciers and on the climate in general.

Zwally tells me that Steffen has a NASA grant to return to the ice cap with a helicopter later in the summer, when the melting is at its peak. "He's bringing a fiber-optic camera with a half-mile-long (kilometers-long) tether," he says with a certain hint of envy. "He's going to put this thing down a moulin. It will be very cool."

Coolness aside, there is the very real possibility that Steffen will discover something in these moulins that will fill in critical gaps in our understanding of how climate change is affecting Greenland, and vice versa. He might, for example, be able to link up the soaring temperatures in Swiss Camp to the instability of the glaciers, and that instability to the clogged Jakobshavn Icefjord, the halibut-filled currents of Ilulissat, and eventually the icebergs banging into the docks in Aasiaat. What's really cool—but just as terrifying—is how fast all of this is happening and how quickly scientists such as Zwally and Steffen have to move just to stay on top of it from year to year.

A shout from up-glacier breaks the climate-change lesson. The team has drilled a successful hole. But it's four in the afternoon and the ice is melting at its quickest now. Zwally tells me that it's time to move fast.